The present invention relates to an ink jet image forming method using ink of two or more kinds (for example, quickly drying ink and slowly drying ink) in combination, and an ink jet image forming device, and in particular to improvements in image quality by attaining higher resolution.
A common ink jet image forming device (hereinafter referred to as xe2x80x9cink jet printerxe2x80x9d) sequentially performs image formation by discharging drops of ink to surfaces of sheets of recording paper to be fed successively. The sheets of recording paper subjected to image formation are successively discharged to a discharge tray where they are stacked.
Further, there has been proposed the following conventional ink jet printer capable of image formation by using two or more different inks and superimposing all the inks over one another on recording paper.
Japanese Unexamined Patent Publication No. 330086/1993 (Tokukaihei 5-330086 published on Dec. 14, 1993) discloses improvements in a dot formation method in the case of using slowly drying ink and quickly drying ink in combination, the slowly drying black ink having high reproducibility but taking time to dry and the quickly drying black ink drying rapidly but producing low-density print. Specifically, when forming color dots in an area adjacent to an area where black dots are formed, an interface therebetween is formed by superimposing quickly drying black ink or a combination of inks of C (cyan), M (magenta) and Y (yellow) over one another, while forming the other area with slowly drying black ink, thereby enhancing reproducibility in a black color while suppressing exudation in the interface between black dots and color dots.
Further, Japanese Unexamined Patent Publication No. 149036/1995 (Tokukaihei 7-149036 published on Jun. 13, 1995) discloses a technique of using black ink having low permeability to recording paper (slowly drying ink), and inks of C, M and Y, having higher permeability (quickly drying ink). Specifically, it is arranged such that, when forming a color dot area adjacent to an area where black dots are formed, black dots in the black dot area are thinned out and color dots (staggered dots) are formed therein instead. In addition, the publication No. 149036/1995 also discloses formation of black dots over color dots, thereby preventing exudation in the boundaries between the black dot area and the color dot area, while cutting drying time of black dots.
The techniques disclosed in the foregoing two publications, however, require high accuracy in determining a position to discharge quickly drying ink to be applied to the interface between the black area and the color area. Specifically, even when the position to discharge quickly drying ink slightly deviates from a predetermined position of the interface, a boundary line of the interface becomes irregular due to the presence of the quickly drying ink, which results in the reduced resolution of an image. Thus, there has been such a potential risk that quickly drying ink which is discharged so as to suppress exudation of dots and attain superior image quality turns out to be a factor to degrade image quality.
In view of the foregoing problems, it is an object of the present invention to provide an ink jet image forming method and an ink jet image forming device capable of forming an image of superior quality by using a combination of two or more different inks including, for example, quickly drying ink and slowly drying ink, in which deviation which may occur in a discharge position of ink causes no reduction in the resolution of an image.
In order to attain the foregoing object, the ink jet image forming method according to the present invention, which uses a combination of two or more different inks including at least white or clear, colorless quickly drying ink and an ink different from the quickly drying ink, includes the step of applying the white or clear, colorless quickly drying ink and the different ink onto the recording medium either one over another or adjacently.
With the foregoing method, it is possible to largely cut drying time of the different ink. Moreover, depending on a combination of the quickly drying ink and a different ink, an image to be formed with the different ink can be made clearer. More specifically, when adopting slowly drying ink as the different ink to be used in combination with the quickly drying ink, the drying time can be shortened more than when forming dots of the slowly drying ink singly on the recording medium. Further, since a common recording medium such as recording paper is white, the quickly drying ink, which functions as a sort of assistant ink which helps the slowly drying ink to dry, remains unnoticeable, i.e., the quickly drying ink causes no degradation in image quality.
Furthermore, when the quickly drying ink is white ink, and the different ink is color ink having a color other than white, contrast to the white ink makes an image in the color ink clearer, thus attaining superior image quality. Note that, as the color ink, it is desirable to adopt ink having a color of relatively low brightness such as black ink.
Further, a preferable example of the ink jet image forming device of the present invention adopting the foregoing ink jet image forming method performs image formation on a recording medium by using a combination of two or more different inks including at least white or clear, colorless quickly drying ink and an ink different from the quickly drying ink, and further, the device includes ink discharge control means for controlling discharge of the quickly drying ink and the different ink so as to apply the white or clear, colorless quickly drying ink and the different ink onto the recording medium either one over another or adjacently.